The stabilization of soils in order to accommodate roadways and light structures is of worldwide importance, and numerous techniques are used to provide a suitable soil base. When excessive water is the problem and a suitable gradient is available, drains and wells are commonly used.
However, many areas cannot be serviced suitably by mere drainage means, and even if they are, localized conditions including slope, contour, and soil permeability, often forestall such a straight-forward arrangement. This is especially the situation in areas where the water table is quite close to the surface.
Such a large and pervasive problem has occasioned a large number of proposals to stabilize such soils. One of the most prominent and promising processes is the lime/cement column technique, on which this invention is an improvement. It has been widely used in Scandinavia with considerable success.
In this process, an augur is rotated as it is pressed into the soil. The term "augur" as used herein is not intended in the sense of a drill or other tool which removes material from a bore and leaves an open shaft or hole. Removal of material is not done in this process. Instead, the augur is intended to loosen the soil as it enters the structure, and, as it withdrawn, still rotating, it injects lime and cement into the soil, either dry or as a slurry, stirring this total mixture as it rises to the surface. Thereafter the material sets up as a solid column, and as such stabilizes the soil structure.
For its major applications this is not a small scale operation. The machinery used for practical application is very large and very powerful. Depths of in-situ pilings up to 60 feet, with diameters up to 4 feet are regularly accommodated. It is a rapid process, usually taking less than five minutes to form a 60 foot deep in-situ piling.
A logical process, and one which has been extensively used, is to inject a slurry of water, lime and cement into the soil while the augur is being withdrawn. A major problem with this system is that a large mixing device must accompany the augur. It requires water, lime and cement, and must be cleaned at least daily. It is a large and undesirable appendage. And then, what if the soil is already quite wet.? In such event a slurry injected into a very wet soil might not set up appropriately, having an unsuitable stoichiometric ratio when mixed with water already present in the soil. Accordingly, a process which injects a slurry into the soil involves extra equipment and is limited in its applicability.
Then suppose that dry lime and cement are infected into the soil, rather than as part of a slurry. Then there may not be sufficient water to react with the lime and cement. While such an arrangement would dispense with the slurry operation, it would not necessarily provide a proper mixture for the entire depth of the in-situ piling.
Accordingly, it is an object of this invention for the augur to provide water to the soil in a proper amount when combined with water already present as the augur is pressed into the structure. Thereafter as the augur is removed, it supplies dry lime and dry cement to the soil to provide a stoichiometric mix which will set up to form a useful in-situ piling.
With this process, water in an appropriate amount is injected into the soil separately from the lime and cement. The water is injected and stirred into the soil on the way down, and the lime and cement are infected and stirred into the soil/water mixture on the way up. There need be no slurry unit, and there is no need for cleanup. The water, lime, and cement are kept dry and separate from water until they are injected.